The present invention relates to a silver halide photographic light-sensitive material. In particular, the present invention relates to an ultrahigh contrast negative type photographic light-sensitive material suitable as a silver halide photographic light-sensitive material used for a photomechanical process.
In photomechanical processes used in the field of graphic arts, used is a method in which photographic images of continuous tone are converted into so-called dot images in which variable image density is represented by sizes of dot areas, and such images are combined with photographed images of characters or line originals to produce printing plates. For silver halide photographic light-sensitive materials used for such a purpose, ultrahigh contrast photographic characteristic enabling clear distinction between image portions and non-image portions has been required in order to obtain favorable reproducibility of characters, line originals and dot images.
As a system responding to such a requirement, there has been known the so-called lithographic development method in which a silver halide light-sensitive material comprising silver chlorobromide is processed with a hydroquinone developer having an extremely low effective concentration of sulfite ions to form images of high contrast. However, in this method, the developer is extremely unstable against oxidation by air since the sulfite ion concentration in the developer is extremely low, and therefore a lot of developer must be replenished in order to stably maintain the developer activity.
As image forming systems in which the instability of the image formation according to the lithographic development method is eliminated and light-sensitive materials are processed with a developer showing good storage stability to obtain ultrahigh contrast photographic characteristic, there can be mentioned those described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,269,922, 4,272,606, 4,311,781, 4,332,878, 4,618,574, 4,634,661, 4,681,836, 5,650,746 and so forth. These are systems in which a silver halide photographic light-sensitive material of surface latent image type containing a hydrazine derivative is processed with a developer containing hydropuinone/metol or hydroquinone/phenidone as main developing agents and 0.15 mol/l or more of sulfite preservative and having pH of 11.0-12.3 to form ultrahigh contrast negative images having a gamma of 10 or higher. According to these systems, photographic characteristics of ultrahigh contrast and high sensitivity can be obtained, and because sulfite can be added to the developer at a high concentration, stability of the developer to air oxidation is markedly improved compared with conventional lithographic developers.
In order to form sufficiently ultrahigh contrast images with use of a hydrazine derivative, it is necessary to perform processing with a developer having pH of 11 or higher, usually 11.5 or higher. Although it becomes possible to increase the stability of the developer by use of a sulfite preservative at a high concentration, it is necessary to use such a developer of high pH as described above in order to obtain ultrahigh contrast photographic images, and the developer is still likely to suffer from air oxidation and instable even with the presence of the preservative. Therefore, various attempts have been made in order to realize ultrahigh images with a lower pH to further improve stability of the developer.
For example, U.S. Pat. No. 4,269,929 (Japanese Patent Laid-open Publication (Kokai, henceforth referred to as xe2x80x9cJP-Axe2x80x9d) No. 61-267759), U.S. Pat. No. 4,737,452 (JP-A-60-179734), U.S. Pat. Nos. 5,104,769, 4,798,780, JP-A-1-179939, JP-A-1-179940, U.S. Pat. Nos. 4,998,604, 4,994,365 and JP-A-8-272023 disclose methods of using a highly active hydrazine derivative and a nucleation accelerator in order to obtain ultrahigh images by using a developer having pH of less than 11.0.
However, silver halide photographic light-sensitive materials used for such image-forming systems have problems concerning processing stability, for example, due to exhaustion of processing solutions, activities of hydrazine compound and nucleation accelerator vary and thus sensitivity fluctuates. As means for improving processing stability, use of an emulsion providing a higher contrast can be mentioned. However, it causes a problem that use of an emulsion providing a higher contrast causes reduction of sensitivity. Therefore, it has been desired to develop a technique for obtaining higher sensitivity with superior processing stability.
Considering these problems of the conventional techniques, an object of the present invention is to provide a silver halide photographic light-sensitive material that provides high contrast and high sensitivity.
As a result of various researches of the inventors of the present invention, they found that a superior silver halide photographic light-sensitive material could provided by using a particular silver halide emulsion to provide a gamma exceeding a certain level, and thus accomplished the present invention.
That is, the present invention provides a silver halide photographic light-sensitive material comprising at least one silver halide emulsion layer on a support, wherein 40 mol % or more, preferably 45-75 mol % of silver halide contained in the silver halide emulsion layer is silver bromide and the silver halide contains 1xc3x9710xe2x88x926 mole or more, preferably 5xc3x9710xe2x88x926 mole to 5xc3x9710xe2x88x923 mole per mole of silver of a metal complex containing one or more cyanide ligands, and the silver halide photographic light-sensitive material has a characteristic curve drawn in orthogonal coordinates of logarithm of light exposure (x-axis) and optical density (y-axis) using equal unit lengths for the both axes, on which gamma is 4.0 or more for the optical density range of 0.1-1.5.
In the silver halide photographic light-sensitive material of the present invention, the metal complex containing one or more cyanide ligands exists in the inside of silver halide crystals, and preferably 99 mol % or less, more preferably 95 mol % or less, of the total amount of silver contained in the silver halide crystals is contained in the inside of the crystals. Further, the silver halide crystals preferably have an aspect ratio (diameter as circle/thickness) of 2 or less.
At least one of silver halide emulsion layers constituting the silver halide photographic light-sensitive material of the present invention preferably contains at least one spectral sensitization dye represented by the following formula (I), (II), (III), (IV), (V), (VIa) or (VIb). 
In the formula, Y11, Y12, Y13 and Y14 each independently represent xe2x95x90N(R1), an oxygen atom, a sulfur atom, a selenium atom or a tellurium atom, provided that either one of Y13 and Y14 is xe2x95x90N(R1), and Y11, Y12 and Y13 or Y11, Y12 and Y14 do not simultaneously represent a sulfur atom. R11 represents an aliphatic group having a water-solubilizable group and 8 or less carbon atoms, and R1, R12 and R13 each independently represent an aliphatic group, an aryl group or a heterocyclic group. However, at least two of R1, R12 and R13 have a water-solubilizable group. Z11 represents a nonmetallic atom group required to form a 5- or 6-membered nitrogen-containing heterocyclic ring, and the 5- or 6-membered nitrogen-containing heterocyclic ring formed with Z11 may have a condensed ring. W1 represents an oxygen atom, a sulfur atom, xe2x95x90N(R1) or xe2x95x90C(E11)(E12). E11 and E12 each independently represent an electron-withdrawing group. These may bond to each other to form a keto ring or an acidic heterocyclic ring. L11 and L12 each independently represent a substituted or unsubstituted methine group, and l11 represents 0 or 1. M1 represents an ion required to offset the charge of the molecule. n11 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n11 is 0. 
In the formula, Z21 represents a nonmetallic atom group required to form a 5- or 6-membered nitrogen-containing heterocyclic ring, and the 5- or 6-membered nitrogen-containing heterocyclic ring formed with Z21 may have a condensed ring. Y21 and Y22 each independently represent xe2x95x90N(R2), an oxygen atom, a sulfur atom, a selenium atom or a tellurium atom. W2 represents xe2x95x90N (Ar), an oxygen atom, a sulfur atom or xe2x95x90C (E21)(E22). E21 and E22 each independently represent an electron-withdrawing group or a nonmetallic atom group for forming an acidic heterocyclic ring when E21 and E22 bond to each other, and Ar represents an aromatic group or an aromatic heterocyclic group. R21 represents an aliphatic group having 8 or less carbon atoms and a water-solubilizable group, and R2, R22 and R23 each independently represent an aliphatic group, an aryl group or a heterocyclic group. However, at least two of R2, R22 and R23 have a water-solubilizable group. L21, L22, L23 and L24 each independently represent a substituted or unsubstituted methine group, and m21 represents 0 or 1. M2 represents an ion required to offset the charge of the molecule. n21 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n21 is 0. 
In the formula, R31 and R32 each independently represent an alkyl group. However, at least one alkyl group has a water-soluble group. V31, V32, V33 and V34 represent a hydrogen atom or a monovalent substituent. However, the sum of the molecular weight of these substituents (V31, V32, V33 and V34) is 50 or less. L31, L32, L33 and L34 each independently represent a substituted or unsubstituted methine group. M3 represents an ion required to offset the charge of the molecule. n31 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n31 is 0. 
In the formula, R41 represents an alkyl group, an alkenyl group or an aryl group, R42 and R43 each independently represent a hydrogen atom, an alkyl group, an alkenyl group or an aryl group, and R44, R45 and R46 each independently represent an alkyl group, an alkenyl group, an aryl group or a hydrogen atom. L41 and L42 each independently represent a substituted or unsubstituted methine group, and p represents 0 or 1. Z41 represents an atomic group required to complete a 5- or 6-membered heterocyclic ring, and the 5- or 6-membered heterocyclic group formed with Z41 may have a condensed ring. M4 represents an ion required to offset the charge of the molecule. n41 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n41 is 0. The spectral sensitization dye represented by the formula (IV) has at least three water-solubilizable groups. 
In the formula, Z51 and Z52 each independently represent a nonmetallic atom group required to form a 5- or 6-membered nitrogen-containing heterocyclic ring, and the 5- or 6-membered nitrogen-containing heterocyclic ring formed with Z51 or Z52 may have a condensed ring. R51 and R52 each independently represent an alkyl group, a substituted alkyl group or an aryl group. Q51 and Q52 represent a nonmetallic atom group required to together form a thiazolidinone ring or an imidazolidinone ring. L51, L52 and L53 each independently represent a methine group or a substituted methine group. n51 and n52 each independently represent 0 or 1. M5 represents an ion required to offset the charge of the molecule. n53 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n53 is 0. 
In the formula, R61 and R62 each independently represent an alkyl group. R63 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, a benzyl group or a phenethyl group. V6 represents a hydrogen atom, a lower alkyl group, an alkoxy group, a halogen atom or a substituted alkyl group, and p6 represents 1 or 2. Z61 represents a group required to form a 5- or 6-membered nitrogen-containing heterocyclic ring, and the 5- or 6-membered nitrogen-containing heterocyclic ring formed with Z61 may have a condensed ring. m61 represents 0 or 1. M61 represents an ion required to offset the charge of the molecule. n61 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n61 is 0. 
In the formula, R64 and R65 each independently represent an alkyl group. R66 and R67 each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, a benzyl group or a phenethyl group. R68 and R69 each represent a hydrogen atom. R68 and R69 may bond to each other to form an alkylene group. R70 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, a benzyl group or xe2x80x94N(W61) (W62) [W61 and W62 each independently represent an alkyl group or an aryl group, or W61 and W62 may bond to each other to form a 5- or 6-membered nitrogen-containing heterocyclic ring]. Further, R66 and R70 or R67 and R70 may bond to each other, respectively, to form an alkylene group. Z62 and Z63 each independently represent a nonmetallic atom group required to form a 5- or 6-membered nitrogen-containing heterocyclic ring, and the 5-or 6-membered nitrogen-containing heterocyclic ring formed with Z62 or Z63 may have a condensed ring. M62 represents an ion required to offset the charge of the molecule. n62 represents a number required to neutralize the total charge of the molecule. However, when an intramolecular salt is formed, n62 is 0.
The silver halide photographic light-sensitive material of the present invention preferably contains a hydrazine derivative. Further, the silver halide photographic light-sensitive material preferably has a membrane surface pH of 6.0 or less for the emulsion layer side. The silver halide photographic light-sensitive material of the present invention can be processed with a developer prepared by using a solid processing agent.
According to the present invention, there can be provided a high contrast silver halide photographic light-sensitive material showing high sensitivity and superior processing stability.